Question

A compound with empirical formula AB has its vapour density 2 times its empirical formula weight. Determine its molecular formula.

Answer 1

Let the empirical formula be AB.

Let its empirical formula weight be E.

Given, Vapour density = 2E

We know, Molecular mass = 2 × Vapour density

= 2 × 2E

= 4E

Now, n = `"Molecular mass"/"Empirical formula weight"`

= `(4E)/E`

= 4

Hence, the molecular formula is (AB)₄​ = A_4​B_4​​